A study on the impact mechanism of safety capacity in petrochemical base is carried out, according to system structure modeling and system dynamics simulation. The hierarchical structure model of 14 factors that affect the safety capacity in petrochemical base is built up. Safety management and emergency management are included in the first hierarchy. In the next hierarchy, there are three factors􀀄monitoring early warning, fire protection and medical safeguard. Traffic conditions, store layout, dock layout, channel water conditions are involved in the third hierarchy. All the rest factors including topographical conditions, meteorological conditions, population distribution, types and harm of hazardous chemical are classified as the base hierarchy. Digital variables are extracted from 14 factors on the basis of the mathematical simulation model of the feedback system. In addition, the mathematical relationship is established among these factors with the actual operating conditions. Then impact characteristics and mechanism of different factors on safety capacity in petrochemical base are summarized to propose the practical short-term portfolio to increase safety capacity in petrochemical base.